1. Field of the Invention
The invention relates to a method and apparatus for the preparation of mineral mixtures, particularly of rough washed coal, in a jig controlled by compressed air, and more particularly to techniques for moving the separating liquid up and down periodically through the openings of the settling material carrier with the aid of control valves arranged in the feed conduits for air and/or separating liquid.
2. Description of the Prior Art
Techniques for preparing mineral mixtures in a jig are well known in the art, in the German published patent application No. 1,147,542, the control of valves arranged in the feed conduits for air is effected with the aid of a rotating cam shaft which periodically opens and closes the valves. In this known valve control, however, it is disadvantageous that an adjustment of the chance of the cam shaft must be undertaken in order to change the frequency of the settling thrust necessary for the settling operation. This leads to undesirable interruptions in the operation of the settling tank, as the adjustment of the cam shaft cannot be undertaken during operation of the apparatus. The same holds true for the jig valve operation disclosed in U.S. Pat. No. 3,252,574.